address comments

repl/scala-2.11/src/test/scala/org/apache/spark/repl/SingletonReplSuite.scala

@@ -55,7 +55,7 @@ class SingletonReplSuite extends SparkFunSuite {
     val classpath = paths.map(new File(_).getAbsolutePath).mkString(File.pathSeparator)
 
     System.setProperty(CONF_EXECUTOR_CLASSPATH, classpath)
-    Main.conf.set("spark.master", "local-cluster[2,4,4096]")
+    Main.conf.set("spark.master", "local-cluster[2,1,1024]")
     val interp = new SparkILoop(
       new BufferedReader(new InputStreamReader(new PipedInputStream(in))),
       new PrintWriter(out))
@@ -68,6 +68,7 @@ class SingletonReplSuite extends SparkFunSuite {
     thread = new Thread(new Runnable {
       override def run(): Unit = Main.doMain(Array("-classpath", classpath), interp)
     })
+    thread.setDaemon(true)
     thread.start()
 
     waitUntil(() => out.toString.contains("Type :help for more information"))
@@ -85,23 +86,26 @@ class SingletonReplSuite extends SparkFunSuite {
   }
 
   private def waitUntil(cond: () => Boolean): Unit = {
-    var i = 0
-    while (i < 100 && !cond()) {
-      Thread.sleep(500)
-      i += 1
-    }
-    if (i == 100) {
-      throw new IllegalStateException("timeout after 50 seconds, current output: " + out.toString)
+    import scala.concurrent.duration._
+    import org.scalatest.concurrent.Eventually._
+
+    eventually(timeout(50.seconds), interval(500.millis)) {
+      assert(cond(), "current output: " + out.toString)
     }
   }
 
+  /**
+   * Run the given commands string in a globally shared interpreter instance. Note that the given
+   * commands should not crash the interpreter, to not affect other test cases.
+   */
   def runInterpreter(input: String): String = {
     val currentOffset = out.getBuffer.length()
-    // append a `val _result = 1` statement to the end of the given code, so that we can know what's
+    // append a special statement to the end of the given code, so that we can know what's
     // the final output of this code snippet and rely on it to wait until the output is ready.
-    in.write((input + s"\nval _result = 1\n").getBytes)
+    val timestamp = System.currentTimeMillis()
+    in.write((input + s"\nval _result_$timestamp = 1\n").getBytes)
     in.flush()
-    val stopMessage = s"_result: Int = 1"
+    val stopMessage = s"_result_$timestamp: Int = 1"
     waitUntil(() => out.getBuffer.substring(currentOffset).contains(stopMessage))
     out.getBuffer.substring(currentOffset)
   }